Older, more established FCC catalyst regeneration techniques are operated in an incomplete mode of combustion. This invention is concerned with such modes of operation. These systems are usually referred to as "standard regeneration" wherein a relatively large amount of coke is left on the regenerated catalyst which is passed from an FCC regeneration zone to an FCC reaction zone. The content of CO in the regeneration zone is relatively high, i.e., 1 to 6 volume percent. The concentration of carbon is approximately 0.25 to 0.45 weight percent carbon on the regenerated catalyst. In U.S. Pat. No. 4,435,282, issued to Bertolacini et al, a system for substantially complete combustion of coke on an FCC molecular sieve catalyst is disclosed. In the regenerator, hydrocarbon conversion catalyst particles are associated with particles of a platinum group metal, an oxidation catalyst, which promotes the combustion of carbon monoxide to carbon dioxide. The gaseous effluent from such a regeneration operated in a "full combustion mode" has a low CO content and a high CO.sub.2 content. The catalyst particles in an FCC process are finely divided particulate solids having a size of between 20 microns and 150 microns to insure adequate fluidization. U.S. Pat. Nos. 4,153,535, 4,221,677, and 4,238,371 issued to Vasalos et al concern the operation of a cyclic, fluidized, catalytic cracking process with a reduction in the emission of CO and SO.sub.x. A metallic promoter is incorporated into a molecular sieve-type cracking catalytic such that a stable sulfur-containing compound forms on the solid particles in the regeneration zone and a sulfur-containing gas is then withdrawn in a downstream sulfur stripping zone.
Nitrogen sensitivity of a hydrocracking catalyst has been found to be negated by introducing into the hydrocracking zone a halogen-containing compound and water with the hydrocarbonaceous feed. See Stine et al, U.S. Pat. No. 3,058,906. A number of U.S. patents issued to Chevron in the late 1970's and early 1980's concern catalytic conversion of nitrogen oxides to thereby control the nitrogen oxide levels in a flue gas generated by a catalyst regenerator.
In U.S. Pat. No. 4,204,945, a process is disclosed for removal of carbon monoxide and sulfur oxides from a flue gas of a catalyst regenerator of an FCC system. Sufficient molecular oxygen is introduced into the catalyst regenerator to provide an atmosphere having a molecular oxygen concentration of at least 0.1 volume percent. A particular carbon monoxide combustion promoter is physically admixed with the cracking catalyst to provide for total consumption of the coke to CO.sub.2. Sulfur oxides in the regenerator off gas are contacted with a silica-free alumina to form a sulfur-containing solid on the catalyst and thereafter hydrogen sulfide in the cracking reactor. In U.S. Pat. No. 4,204,944 issued to the same patentees, Flanders et al, a process is provided for an FCC unit having a non-zeolitic crystalline refractory inorganic oxide catalyst. The amount of carbon monoxide and sulfur oxides in the regenerator flue gas is reduced by reacting carbon monoxide and oxygen to carbon dioxide in the presence of a carbon monoxide oxidation promoter, inclusive of platinum. Sulfur and an alumina-containing solid are present wherein sulfur trioxide is reacted with alumina and thereafter hydrogen sulfide is formed in the cracking zone by contact of the sulfur and alumina-containing solid with the hydrocarbon feed stream. Similar techniques are provided in U.S. Pat. Nos. 4,115,250 and 4,115,251, Flanders et al, for the reduction of pollution emissions using an alumina-containing catalyst in association with a CO promoter.
NO.sub.x is controlled in the presence of a platinum-promoted complete combustion regenerator in U.S. Pat. No. 4,290,878, issued to Blanton. Recognition is made of the fact that the CO promoters result in a flue gas having an increased content of nitrogen oxides. These nitrogen oxides are reduced or suppressed by using, in addition to the CO promoter, a small amount of an iridium or rhodium compound sufficient to convert NO.sub.x to nitrogen and water.
Both catalytic and non-catalytic addition of ammonia to a flue gas system has been utilized to reduce NO.sub.x. Usually the non-catalytic method includes the injection of ammonia to a NO.sub.x -containing stream at temperatures greater than 1300.degree. F. Exemplary of this type of process is Dean et al, U.S. Pat. No. 4,624,840, wherein ammonia is injected into a combustion effluent stream at a temperature of 1300.degree.K. to 1600.degree.K. at a point where the stream is cooling at a rate of at least 250.degree.K. per second. See also U.S. Pat. No. 4,507,269 issued to the same patentees. Trapped cracking catalyst fines and ammonia are injected to a sulphur oxide and nitrogen oxide effluent stream to remove nitrogen oxides in Dimpfl et al, U.S. Pat. No. 4,434,147. Where an excess stoichiometric amount of ammonia is added to the flue gas system, a situation evolves, known as "ammonia breakthrough", whereby unreacted ammonia is emitted to the atmosphere as a pollutant. In order to reduce the ammonia breakthrough problem, U.S. Pat. No. 4,423,017, Dean, discloses the use of an additional reducing gas and placement of metallic material at the end of the reduction zone maintained at a temperature of 700.degree. C. to 1100.degree. C. In non-catalytic ammonia addition systems, excess ammonia over that required to vitiate the quantity of NO.sub.x can be oxidized to NO.sub.x by the subsequent addition of secondary air. However, Brogan, U.S. Pat. No. 4,335,084, discloses that this subsequent addition of air will not convert excess ammonia to NO.sub.x if the temperature in the air injection zone is below 2400.degree. F. Caution is, however, expressed that the temperature must not fall below 1900.degree. F. because of freeze-out problems with CO at temperatures below 1900.degree. F.
Exemplary of catalytic systems where ammonia is added to convert NO.sub.x to nitrogen and water vapor are U.S. Pat. Nos. 4,164,546, 4,104,361, and 4,002,723. The first of these patents, issued to Welty Jr. et al, describes the use of a copper oxide on alumina catalyst and generically described as a Group IB, Group VIB, Group VIIB, or Group VIII metal. The latter of these references, issued to Inaba et al, discloses the use of a copper on alumina catalyst with the presence of an alkali metal or an alkali earth metal with the optional presence of a small amount of a precious metal such rhodium, ruthenium, platinum or pallidium. The alkali metal content of these catalysts is important in the conversion of ammonia and NO.sub.x to nitrogen and water vapor as exemplified in U.S. Pat. No. 4,104,361 issued to Nishikawa et al wherein the alkali metal content of a zeolite is controlled through ion exchange with an alkaline earth metal compound before deposit of a noble metal catalyst and a base metal of copper, iron, vanadium, chromium or molybdenum onto the alumina. Nitrogen oxide in a fluidized bed can also be reduced by the direct introduction of ammonia into the fluidized bed as disclosed in Gumerman, U.S. Pat. No. 4,181,705.
Another process technique to reduce the amount of NO.sub.x in a flue gas was described in U.S. Pat. No. 4,521,388, Samish et al, wherein a flue gas stream is split and only one of the streams is treated with ammonia and NO.sub.x to remove NO.sub.x therefrom, and thereafter combining the streams. By treating only a portion of the flue gas, the amount of catalyst required to perform the NO.sub.x reduction is reduced while residual NO.sub.x and ammonia contents of the recombined streams is controlled to a desired level. Recognition is made in U.S. Pat. No. 4,351,811, Matusda et al, of a reduction process of NO.sub.x with ammonia. In order to obtain a proper stoichimetric quantity of NO.sub.x to ammonia, the concentration of NO.sub.x is adjusted by addition of predetermined amounts of NO or NO.sub.2 to the gas to be treated. The patentees describe a process where the quantity of ammonia added is 0.8 to 2.0 mole times as large as the total quantity of NO and NO.sub.2 in the gas to be treated. By making the quantity of additive ammonia as small as possible with respect to the quantity of NO.sub.x, then unreacted ammonia contained in the process exhaust gas can be suppressed to a small quantity.
In Matthews, U.S. Pat. No. 4,368,057, a process is disclosed for converting NH.sub.3 to N.sub.2 by adding a sufficient amount of NO.sub.x. The NH.sub.3 -containing stream is a pre-combustion stream derived from coal gasification and not in an FCC reactor-regenerator process scheme. Japanese patent No. J7 9030-318, Hitachi, disclosed mixing an ammonia-containing gas with NO.sub.x and then contacting with a catalyst to remove the ammonia by reaction with NO.sub.x. The prior art has failed to recognize the problems of ammonia content in a partial combustion mode regeneration zone and has failed to recognize that this residual quantity of ammonia, when passed through a CO boiler to convert CO to CO.sub.2, will result in an increase in NO.sub.x production.